Braided stent with expansion ring and method of delivery

ABSTRACT

A self-expanding braided stent includes at least a distal radial expansion ring added to a distal end of the stent body to increase a radial expansion force of the self-expanding braided stent in deployment of the stent, and to facilitate advancement of the stent through a delivery sheath by a core advancement wire. A proximal radial expansion ring is optionally added to a proximal end of the stent body to allow the stent to be recaptured following partial deployment by retraction of the core advancement wire, prior to full deployment of a proximal portion of the stent body.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional application that claims priority to U.S. patent application Ser. No. 13/802,114 entitled “Braided stent with expansion ring and method of delivery” and filed Mar. 13, 2013, the contents of which are incorporated herein by reference in their entirety as if set forth verbatim.

BACKGROUND OF THE INVENTION

This invention relates generally to devices for interventional therapeutic treatment or vascular surgery for treatment of defects in the vasculature, and more particularly concerns a system and method for delivering a self-expanding braided stent to a treatment site in a vasculature of a patient.

Stents, which are tubular reinforcements inserted into a blood vessel to provide an open path within the blood vessel, have been widely used in intravascular angioplasty treatment of occluded cardiac arteries. In such applications, the stent is inserted after an angioplasty procedure or the like in order to prevent restenosis of the artery. In these applications, the stents are often deployed by use of inflatable balloons, or mechanical devices which force the stent open, thereby reinforcing the artery wall and provide a clear through-path in the center of the artery after the angioplasty procedure to prevent restenosis.

While such procedures may be useful in certain aspects of vascular surgery in which vasoocclusive devices are used, the weakness and tortuosity of the neurovasculature places limits on the applicability of such stents in procedures to repair neurovascular defects. Furthermore, the use of placement techniques, such as balloons or mechanical expansions of the type often found to be useful in cardiac surgery, are relatively less useful in vasoocclusive surgery, particularly when tiny vessels, such as those found in the brain, are to be treated. Hence, those skilled in the art have recognized a need for a stent compatible with techniques in vasoocclusive treatment of neurovascular defects that provides selective reinforcement in the vicinity of a neurovascular defect, while avoiding any unnecessary trauma or risk of rupture to the blood vessel.

Braided stents, typically formed from a plurality of elongate members, such as two or more metal wires, or polymeric fibers or strands of material, for example, can be very useful in treatment of neurovascular defects. However, one of the problems in deploying a self-expanding braided stent in a body lumen is activation of the initially expanding end, typically the distal end of the braided stent, to fully open. It is important that the initially expanding end should open fully, easily, and quickly, so that the rest of the length of self-expanding braided stent can be deployed, using the initially expanding end as an anchor point.

Stents made of braided wire also commonly have a high internal friction that resists the inherent radial expansion force of the self-expanding braided stent to open, particularly resisting opening of the initially expanding end, which can cause problems in anchoring and deployment of such self-expanding braided stents. Another common problem with deployment of braided stents is difficulty in advancing the compressed or crimped braided stent through a delivery sheath or microcatheter, typically also due to friction between the braided stent and the delivery sheath or microcatheter. Traditional delivery systems for braided stents push the braided stent in a distal direction by advancing a blunt surface against a proximal end of the braided stent, and consequently the application of force on the proximal end of the braided stent tends to axially compress the braided stent, causing the braided stent to expand radially. As a result, as the braided stent expands within the delivery sheath or microcatheter, an increased normal force is applied to the inner surface of the delivery sheath or microcatheter, increasing friction between the braided stent and the delivery sheath or microcatheter.

Current self-expanding braided stents typically depend solely on their material, dimension, cell design, and internal friction to expand. Deployment of such self-expanding braided stents commonly requires extra manipulation by a user to fully open the self-expanding braided stents, which affects placement accuracy and adds risk to the procedure. Proper deployment and fixation of the initial deployment end or distal end of a self-expanding braided stent are necessary for the subsequent proper alignment and positioning of the remainder of the stent body.

Another problem with deployment of self-expanding braided stents involves difficulty in recapturing a self-expanding braided stent after partial deployment and prior to full deployment of the stent. Currently, a self-expanding braided stent typically is advanced through a delivery sheath or microcatheter until the self-expanding braided stent emerges. When the self-expanding braided stent is unrestrained outside of the sheath or microcatheter, the self-expanding braided stent typically then expands and is deployed in the vasculature, making recapturing of the self-expanding braided stent difficult. self-expanding braided stent with increased radial expansion force, particularly at the initial deployment end or distal end, that can also reduce the internal friction of the braided stent during delivery of the braided stent through a delivery sheath or microcatheter, for improved ease and reliability of deployment of the self-expanding braided stent, particularly at the initial deployment end or distal end of the self-expanding braided stent.

It also would be desirable to provide an improved self-expanding braided stent that can be recaptured following partial deployment of a distal portion of the self-expanding braided stent prior to full deployment of a later deployed portion or proximal portion of the self-expanding braided stent. The present invention meets these and other needs.

SUMMARY OF THE INVENTION

Briefly and in general terms, the present invention provides for an improved self-expanding braided stent with one or more expansion rings, and methods of delivering the self-expanding braided stent through a delivery sheath or microcatheter to a treatment site in a patient's vasculature. The present invention provides for the addition of at least one radial expansion ring to an initial deployment end or distal end of a self-expanding braided stent to increase a radial expansion force of the self-expanding braided stent, for improved ease and reliability of deployment of the self-expanding braided stent, and particularly more reliable expansion and fixing of the initial deployment end or distal end of the self-expanding braided stent in deployment of the self-expanding braided stent. The addition of a radial expansion ring to a later deployed end or proximal end of a self-expanding braided stent allows the self-expanding braided stent to be recaptured following partial deployment of a distal portion of the self-expanding braided stent, and prior to full deployment of a later deployed portion or proximal portion of the self-expanding braided stent.

Accordingly, in a first embodiment, the present invention provides for a braided stent, including a tubular braided stent body formed from a plurality of elongate members, and one or more expansion rings disposed within and fixedly connected to at least one of the proximal end and the distal end of the tubular braided stent body. In a presently preferred aspect, the one or more expansion rings have a compressed configuration having a first diameter and an expanded configuration having a second diameter larger than the first diameter. In another presently preferred aspect, the plurality of elongate members may be formed by a plurality of metal wires, a plurality of polymeric fibers, a plurality of strands of material, or the like. In another presently preferred aspect, the braided stent is a self-expanding stent having a compressed configuration having an unexpanded diameter and an expanded configuration having an expanded diameter larger than the first diameter.

In another presently preferred aspect, the one or more expansion rings include a plurality of elongated connecting arm members having first ends at the first end of the one or more expansion rings and second ends at the second end of the expansion ring, and the plurality of elongated connecting arm members are connected sequentially to adjacent ones of the plurality of elongated connecting arm members alternatingly at the first and second ends to form a plurality of alternating elbow connections at the first and second ends, such as in a zigzag configuration, for example. In another presently preferred aspect, the one or more expansion rings are formed of shape memory material, such as a nickel titanium alloy or a shape memory polymer, for example, having a shape memory position in the expanded configuration. Preferably the one or more expansion rings is heat treated so that the shape memory position is an expanded zigzag type ring, and the plurality of elongated connecting arm members and the alternating elbow connections preferably are configured to be compressed into a small tubular shape during delivery. In another presently preferred aspect, the one or more expansion rings include a plurality of attachment tabs connected to the plurality of alternating elbow connections at the first ends of the one or more expansion rings, and preferably the plurality of alternating elbow connections at the first ends of the one or more expansion rings have exterior ends directed away from the plurality of elongated connecting arm members, and the plurality of attachment tabs are connected to the exterior ends of the plurality of alternating elbow connections at the first ends of the one or more expansion rings. The plurality of attachment tabs preferably are fixedly attached to the tubular braided stent body, such as by welding, soldering or gluing the attachment tabs to an expansion ring, for example. Alternatively, the attachment tabs can include holes in them so that a wire loop can be threaded through the attachment tabs, as well as through interstices of the braided stent to connect the attachment tabs and the braided stent together. In addition, two or more attachment tabs can be included at the ends of each elbow of the expansion ring, and the attachment tabs can then be used to capture a portion of the braided stent between them, after which the two or more attachment tabs can be secured together to be permanently secured to the braided stent by welding, soldering, adhesive, or the like. In another presently preferred aspect, an expansion ring is disposed within and fixedly connected to the initial deployment end or distal end of the tubular braided stent body, and a proximal expansion ring optionally also may be disposed within and fixedly connected to the later deployed end or proximal end of the tubular braided stent body.

In another presently preferred aspect, a core advancement wire is provided that is disposed within and extends through the lumen of the tubular braided stent body and the lumen of a distal expansion ring, and when a proximal expansion ring is provided, the core advancement wire extends through the lumen of the proximal expansion ring as well, for delivering and releasing the self-expanding stent through a delivery sheath or microcatheter to a treatment site in a patient's vasculature. The core advancement wire preferably includes a proximal portion, a distal portion, an intermediate portion located between the proximal and distal portions of the core advancement wire, and a stop member positioned between the distal portion and the intermediate portion of the core advancement wire. In a presently preferred aspect, the stop member is formed by an enlarged portion of the core advancement wire having a diameter greater than or equal to the first diameter of the compressed configuration of the expansion member. In another presently preferred aspect, the stop member is configured to engage a proximal, interior side of the distal expansion ring when the core advancement wire is advanced distally, whereby force applied distally to the core advancement wire is transmitted through the distal expansion ring to the initial deployment end or distal end of the braided stent and acts to drag and elongate the braided stent distally. The braided stent is typically configured to be delivered through the delivery sheath or microcatheter, and the core advancement wire is preferably configured to reduce friction of the braided stent with the delivery sheath or microcatheter when force is applied distally to the core advancement wire.

In another presently preferred aspect, when a proximal expansion ring is provided, the core advancement wire includes an intermediate stop member on the core advancement wire positioned on the intermediate portion of the core advancement wire within the lumen of the braided stent distal to the second expansion ring. In a presently preferred aspect, the intermediate stop member includes an enlarged portion of the core advancement wire having a diameter greater than or equal to the first diameter of the compressed configuration of the second expansion member.

In another presently preferred aspect, the present invention provides for a method of delivering and releasing the self-expanding stent through a delivery sheath or microcatheter to a treatment site in a patient's vasculature, including the step of advancing the core advancement wire distally such that the distal stop member engages a proximal, interior side of the distal expansion ring, whereby force applied distally to the core advancement wire is transmitted through the distal expansion ring to the initial deployment end or distal end of the tubular self-expanding braided stent acting to drag and elongate the tubular self-expanding braided stent, reducing friction of the tubular self-expanding braided stent with the delivery sheath or microcatheter when force is applied distally to the core advancement wire. In another presently preferred aspect, the method includes the steps of dragging the distal expansion member of the tubular self-expanding braided stent distally of the delivery sheath or microcatheter while retaining the proximal expansion member of the tubular self-expanding braided stent within the delivery sheath or microcatheter, retracting the core advancement wire proximally such that the intermediate stop member engages a distal, interior side of the proximal expansion ring, retracting the initial deployment end or distal end of the tubular self-expanding braided stent within the delivery sheath or microcatheter such that the distal expansion member and the initial deployment end or distal end of the tubular self-expanding braided stent are reduced in diameter, and recapturing the tubular self-expanding braided stent within the delivery sheath or microcatheter.

These and other features and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments in conjunction with the accompanying drawings, which illustrate, by way of example, the operation of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an expansion ring configured to be affixed within a braided stent, according to the invention.

FIG. 2 is a cross-sectional schematic elevational view of an expansion ring of FIG. 1 affixed within an initial deployment end or distal end of a braided stent, shown contained within a delivery sheath or microcatheter, according to the invention.

FIG. 3 is a cross-sectional schematic elevational view similar to FIG. 2 , showing partial deployment of the initial deployment end or distal end of the braided stent from the delivery sheath or microcatheter of FIG. 2 .

FIG. 4 is a cross-sectional schematic elevational view of an expansion ring of FIG. 1 affixed within an initial deployment end or distal end of a braided stent, shown contained within a delivery sheath or microcatheter, and including an advance wire extending through the braided stent and expansion ring, according to the invention.

FIG. 5 is a cross-sectional schematic elevational view similar to FIG. 4 , showing partial deployment of the initial deployment end or distal end of the braided stent from the delivery sheath or microcatheter of FIG. 4 .

FIG. 6 is a cross-sectional schematic elevational view of a braided stent having a distal expansion ring and a proximal expansion ring affixed within the distal and proximal ends of the braided stent, shown contained within a delivery sheath or microcatheter, and including an advance wire extending through the braided stent and expansion ring, according to the invention.

FIG. 7 is a cross-sectional schematic elevational view similar to FIG. 6 , showing partial deployment of the initial deployment end or distal end of the braided stent from the delivery sheath or microcatheter of FIG. 6 .

FIG. 8 is a cross-sectional schematic elevational view similar to FIG. 6 , showing retraction of the initial deployment end or distal end of the braided stent into the delivery sheath or microcatheter of FIG. 6 .

FIG. 9 is a cross-sectional schematic elevational view similar to FIG. 6 , showing implantation of a braided stent at a treatment site in a patient's vasculature, and withdrawing of the advance wire and delivery sheath or microcatheter.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

While stents have commonly been delivered in in blood vessels such as during intravascular angioplasty treatment of occluded cardiac arteries, by use of inflatable balloons or mechanical devices that force a stent open, the weakness and tortuosity of the neurovasculature places limits on the applicability of such stents in procedures to repair neurovascular defects, and it is desirable to provide an improved self-expanding braided stent with increased its radial expansion force, particularly at the initial deployment end or distal end, that can also reduce the internal friction of the braided stent during delivery of the braided stent through a delivery sheath or microcatheter, that can be more reliably expanded and fixed at the initial deployment end or distal end of the self-expanding braided stent, and that can be recaptured following partial deployment of a distal portion of the self-expanding braided stent prior to full deployment of a later deployed portion or proximal portion of the self-expanding braided stent.

Accordingly, referring to the drawings, which are provided by way of example, and not by way of limitation, in a first embodiment, for treatment of a patient's vasculature, the present invention provides for a braided stent 10 including a tubular braided stent body 11, having a later deployed end or proximal end 12, an initial deployment end or distal end 14, and an inner lumen 16. The tubular braided stent body is preferably formed from a plurality of elongate members 18, typically formed from two or more metal wires, or polymeric fibers or strands of material, for example. In a presently preferred aspect, the braided stent is a self-expanding stent, and includes one or more expansion rings 20, each having a first end 22, a second end 24, and an inner lumen 26. The one or more expansion rings preferably are disposed within and fixedly connected to at least the initial deployment end or distal end of the tubular braided stent body, although one or more expansion rings may also be disposed within and fixedly connected to the later deployed end or proximal end of the tubular braided stent body, as will be further explained below.

Each expansion ring includes a plurality of elongated connecting arm members 30 having first ends 32 at the first end of the expansion ring, and second ends 34 at the second end of the expansion ring. The plurality of elongated connecting arm members are connected sequentially to adjacent ones of the plurality of elongated connecting arm members alternatingly at the first and second ends to form a plurality of alternating elbow connections 36 at the first and second ends of the expansion ring, so that the plurality of elongated connecting arm members of each expansion ring substantially have a zigzag configuration.

Referring to FIGS. 3 and 4 , each expansion ring preferably is formed to have a compressed configuration 38, having a first diameter, and an expanded configuration 42, having a second diameter that is larger than the first diameter of the compressed configuration of the expansion ring. Each expansion ring is preferably formed of a shape memory material such as a nickel-titanium alloy, or a shape memory polymer, for example, having a shape memory position in the expanded configuration. For example, the expansion rings may be appropriately heat treated so that the expansion ring forms in the desired shape of the expanded shape memory position, with the plurality of elongated connecting arm members having a substantially zigzag type configuration. Each expansion ring is typically formed by cutting a tube formed of a shape memory material such as a nickel-titanium alloy, or a shape memory polymer, for example, by an appropriate laser. The plurality of elongated connecting arm members and the alternating elbow connections preferably can be compressed in the compressed configuration into a tubular shape that is small enough to comfortably fit within and pass through a delivery sheath or microcatheter 44 to allow delivery of the stent through the delivery sheath or microcatheter.

In another presently preferred aspect, each expansion ring includes a plurality of attachment tabs 46 connected to the plurality of alternating elbow connections at the first ends of the expansion ring. The plurality of attachment tabs preferably are connected to exterior ends 48 of the plurality of alternating elbow connections at the first ends of the one or more expansion ring. The plurality of attachment tabs preferably are fixedly connected to a tubular braided stent body, typically at or near a distal or proximal end of the tubular braided stent body, such as by welding, soldering, or gluing by an appropriate adhesive, for example. Alternatively, the attachment tabs can include holes in them so that a wire loop can be threaded through the attachment tabs, as well as through interstices of the braided stent to connect the attachment tabs and the braided stent together. In addition, two or more attachment tabs can be included at the ends of each elbow of the expansion ring, and the attachment tabs can then be used to capture a portion of the braided stent between them, after which the two or more attachment tabs can be secured together to be permanently secured to the braided stent by welding, soldering, adhesive, or the like. At least one first, distal, expansion ring 20 a preferably is disposed within and fixedly connected to the initial deployment end or distal end of the tubular braided stent body. As is illustrated in FIGS. 6-9 , a second, proximal, expansion ring 20 b preferably also is disposed within and fixedly connected to the later deployed end or proximal end of the tubular braided stent body.

Referring to FIGS. 4-9 , in a second embodiment, in which like elements are indicated by like reference numbers, the present invention further provides for an apparatus 50 for delivering and releasing a self-expanding braided stent through a delivery sheath or microcatheter to a treatment site in a patient's vasculature 52. The apparatus includes a braided stent including a tubular braided stent body, described above, and also includes a core advancement wire 54, which is disposed within and extends through the lumen of the tubular braided stent body, and is disposed within and extending through the lumen of the distal expansion ring 20 a fixedly connected within the initial deployment end or distal end of the tubular braided stent body. When a proximal expansion ring 20 b is fixedly connected within the later deployed end or proximal end of the tubular braided stent body, as is illustrated in FIGS. 6-9 , the core advancement wire also is disposed within and extends through the lumen of the proximal expansion ring.

The core advancement wire includes a proximal portion 56, a distal portion 58, an intermediate portion 60 located between the proximal and distal portions of the core advancement wire, and a distal stop member 62 positioned between the distal portion and the intermediate portion of the core advancement wire. In one presently preferred aspect, as is shown in FIG. 4 , the distal stop member is formed as an enlarged portion of the core advancement wire having a diameter greater than or equal to the first diameter of the compressed configuration of the expansion member. The distal stop member is preferably configured to engage a proximal, interior side 64 of the distal expansion ring when the core advancement wire is advanced distally, so that force applied distally to the core advancement wire is transmitted through the distal stop member to the distal expansion ring, and consequently is transmitted to the initial deployment end or distal end of the braided stent, thereby acting to drag the braided stent in a distal direction, as the braided stent is delivered through the delivery sheath or microcatheter to a treatment site, as well as to elongate the braided stent, advantageously also reducing friction with the delivery sheath or microcatheter through which the braided stent is delivered.

In another preferred aspect, a proximal stop member 66 may also be provided on the core advancement wire positioned outside and proximal to the proximal end of the braided stent. When it is provided, the proximal stop member preferably has a diameter greater than or equal to the unexpanded diameter of the compressed configuration of the braided stent and less than a diameter of the delivery sheath or microcatheter.

The self-expanding braided stent can be delivered and released through the delivery sheath or microcatheter to a treatment site in a patient's vasculature by advancing the core advancement wire distally (to the left as shown), so that the distal stop member of the core advancement wire engages the proximal, interior side of the distal expansion ring. Since the distal expansion ring is attached to the braided stent, force applied distally to the core advancement wire is transmitted through the distal expansion ring to the initial deployment end or distal end of the braided stent, and the force applied to the initial deployment end or distal end of the braided stent in the distal direction therefore tends to drag and elongate the stent, consequently reducing the diameter of the compressed configuration of the braided stent, reducing the friction between the braided stent and the delivery sheath or microcatheter.

In another embodiment illustrated in FIGS. 6-9 , in which like elements are indicated by like reference numbers, the present invention further provides for an apparatus for delivering and releasing a self-expanding braided stent through a delivery sheath or microcatheter to a treatment site in a patient's vasculature, in which the core advancement wire also includes an intermediate stop member 68 positioned on the intermediate portion of the core advancement wire, within the lumen of the braided stent distal to the proximal expansion ring. The intermediate stop member preferably is formed as an enlarged portion of the core advancement wire having a diameter that is greater than or equal to the first diameter of the compressed configuration of the proximal expansion member. The intermediate stop member preferably is configured to engage the distal, interior side 70 of the proximal expansion ring when the core advancement wire is retracted proximally, allowing retraction of the braided stent within the delivery sheath or microcatheter.

In this embodiment, the self-expanding braided stent can be delivered and released through the delivery sheath or microcatheter to a treatment site in a patient's vasculature by advancing the core advancement wire distally, as described above, and the core advancement wire may also then be retracted proximally (to the right as shown in FIG. 8 ), so that the intermediate stop member engages the distal, interior side of the proximal expansion ring. As long as the braided stent is not deployed past the proximal expansion ring, the braided stent can be recaptured in this way. The retraction force applied proximally to the delivery wire is transmitted through the proximal expansion ring to the proximal end of the braided stent, and as the braided stent is recaptured back into the delivery sheath or microcatheter, the initial deployment end or distal end of the braided stent is reduced in diameter by the mouth 72 of the sheath or microcatheter until the braided stent is again fully enclosed by the delivery sheath or microcatheter.

It will be apparent from the foregoing that while particular forms of the invention have been illustrated and described, various modifications can be made without departing from the spirit and scope of the invention. Accordingly, it is not intended that the invention be limited, except as by the appended claims. 

We claim:
 1. An apparatus for delivering and releasing a self-expanding braided stent through a delivery sheath to a treatment site in a patient's vasculature, said apparatus comprising: a tubular self-expanding braided stent body having a proximal end, a distal end, and an inner lumen, said tubular self-expanding braided stent body being formed from a plurality of elongate members, said tubular self-expanding braided stent body having a compressed configuration and an expanded configuration; at least one expansion ring disposed within and fixedly connected to said distal end of said tubular self-expanding braided stent body, said at least one expansion ring having a proximal interior end, a distal exterior end, and an inner lumen, said at least one expansion ring having a compressed configuration having a first diameter and an expanded configuration having a second diameter larger than said first diameter, said at least one expansion ring including a plurality of elongated connecting arm members having first ends at said proximal interior end of said at least one expansion ring and second ends at said distal exterior end of said expansion ring, said plurality of elongated connecting arm members being connected sequentially to adjacent ones of said plurality of elongated connecting arm members alternatingly at said first and second ends to form a plurality of alternating elbow connections at said first and second ends having a zigzag configuration, wherein said plurality of elongated connecting arm members and said plurality of alternating elbow connections are configured to be compressed into a small tubular shape during delivery; a core advancement wire disposed within and extending through said inner lumen of said tubular self-expanding braided stent body and said inner lumen of said at least one expansion ring, said core advancement wire having: a proximal portion, a distal portion, an intermediate portion located between said proximal and distal portions of said core advancement wire, an intermediate stop member on said core advancement wire positioned on said intermediate portion of said core advancement wire within said inner lumen of said tubular self-expanding braided stent body, and a distal stop member positioned between said distal portion and said intermediate portion of said core advancement wire and immediately adjacent to said proximal interior end of said at least one expansion ring, said distal stop member being configured to press distally into said proximal interior end of said at least one expansion ring when the said core advancement wire is advanced distally, whereby force applied distally to said core advancement wire is transmitted through said at least one expansion ring to said distal end of said tubular self-expanding braided stent body and acts to drag and elongate said tubular self-expanding braided stent body, and wherein said core advancement wire is configured to reduce friction of said tubular self-expanding braided stent body with said delivery sheath when force is applied distally to said core advancement wire.
 2. The apparatus of claim 1, wherein said at least one expansion ring is formed of shape memory material having a shape memory position in said expanded configuration.
 3. The apparatus of claim 1, further comprising a plurality of attachment tabs connected to said plurality of alternating elbow connections at said proximal interior end of said at least one expansion ring, wherein said plurality of alternating elbow connections at said proximal interior end of said at least one expansion ring have exterior ends directed away from said plurality of elongated connecting arm members and said plurality of attachment tabs are connected to said exterior end of said plurality of alternating elbow connections at said proximal interior ends of said at least one expansion ring, and wherein said plurality of attachment tabs are fixedly attached to said tubular self-expanding braided stent body.
 4. The apparatus of claim 1, wherein said distal stop member comprises an enlarged portion of said core advancement wire having a diameter greater than or equal to said first diameter of said compressed configuration of said at least one expansion ring disposed within and fixedly connected to said distal end of said tubular self-expanding braided stent body.
 5. The apparatus of claim 1, further comprising a second expansion ring having a distal interior end, a proximal exterior end, and an inner lumen, the second expansion ring being disposed within and fixedly connected to said proximal end of said tubular self-expanding braided stent body, said core advancement wire further including a proximal stop member on said core advancement wire positioned outside and proximal to said proximal end of said tubular self-expanding braided stent body, said proximal stop member having a diameter greater than or equal to an unexpanded diameter of a compressed configuration of said second expansion ring and less than a diameter of the delivery sheath.
 6. The apparatus of claim 1, further comprising a second expansion ring having a distal interior end, a proximal exterior end, and an inner lumen, the second expansion ring being disposed within and fixedly connected to said proximal end of said tubular braided self-expanding stent body, said intermediate stop member positioned within said inner lumen of said tubular self-expanding braided stent body distal to said second expansion ring and immediately adjacent to said distal interior end of said second expansion ring.
 7. The apparatus of claim 6, wherein said intermediate stop member comprises an enlarged portion of said core advancement wire having a diameter greater than or equal to a first diameter of a compressed configuration of said second expansion ring.
 8. An apparatus for delivering and releasing a self-expanding stent through a delivery sheath to a treatment site in a patient's vasculature, said apparatus comprising: a tubular self-expanding braided stent body having a proximal end, a distal end, and an inner lumen, said tubular self-expanding braided stent body being formed from a plurality of elongate members, said tubular self-expanding braided stent body having a compressed configuration and an expanded configuration; a distal expansion ring and a proximal expansion ring, said distal expansion ring disposed within and fixedly connected to said distal end of said tubular self-expanding braided stent body, said proximal expansion ring disposed within and fixedly connected to said proximal end of said tubular self-expanding braided stent body, said distal expansion ring having a proximal interior end, a distal exterior end, and an inner lumen, and said proximal expansion ring having a distal interior end, a proximal exterior end, and an inner lumen, each of said distal and proximal expansion rings having a compressed configuration having a first diameter and an expanded configuration having a second diameter larger than said first diameter, each of said distal and proximal expansion rings including a plurality of elongated connecting arm members having first ends at said proximal interior end of said distal expansion ring and said distal interior end of said proximal expansion ring and second ends at said distal exterior end of said distal ring and said proximal exterior end of said proximal expansion ring, said plurality of elongated connecting arm members being connected sequentially to adjacent ones of said plurality of elongated connecting arm members alternatingly at said first and second ends to form a plurality of alternating elbow connections at said first and second ends having a zigzag configuration, wherein said plurality of elongated connecting arm members and said plurality of alternating elbow connections are configured to be compressed into a small tubular shape during delivery; a core advancement wire disposed within and extending through said inner lumen of said tubular self-expanding braided stent body and said inner lumen of said distal and proximal expansion rings, said core advancement wire having: a proximal portion, a distal portion, an intermediate portion located between said proximal and distal portions of said core advancement wire, a distal stop member positioned between said distal portion and said intermediate portion of said core advancement wire within said inner lumen of said tubular self-expanding braided stent body distal to said proximal expansion ring and immediately adjacent to said proximal interior end of said distal expansion ring, said distal stop member being configured to press distally into said proximal interior end of said distal expansion ring when the said core advancement wire is advanced distally, whereby force applied distally to said core advancement wire is transmitted through said distal expansion ring to said distal end of said tubular self-expanding braided stent body and acts to drag and elongate said tubular self-expanding braided stent body, and an intermediate stop member positioned on said intermediate portion of said core advancement wire within said inner lumen of said tubular self-expanding braided stent body distal to said proximal expansion ring and immediately adjacent to said distal interior end of said proximal expansion ring, said intermediate stop member being configured to press proximally into said distal interior end of said proximal expansion ring when said core advancement wire is retracted proximally, allowing retraction of said tubular self-expanding braided stent body within the delivery sheath, wherein said core advancement wire is configured to reduce friction of said tubular self-expanding braided stent body with said delivery sheath when force is applied distally to said core advancement wire.
 9. The apparatus of claim 8, wherein at least one of said proximal expansion ring and said distal expansion ring is formed of shape memory material having a shape memory position in said expanded configuration.
 10. The apparatus of claim 8, further comprising a plurality of attachment tabs connected to said plurality of alternating elbow connections at said proximal interior end of said distal expansion ring and said distal interior end of said proximal expansion ring, wherein said plurality of alternating elbow connections at said proximal interior end of said distal expansion ring and said distal interior end of said proximal expansion ring have exterior ends directed away from said plurality of elongated connecting arm members and said plurality of attachment tabs are connected to said exterior ends of said plurality of alternating elbow connections at said proximal interior end of said distal expansion ring and said distal interior end of said proximal expansion ring, and wherein said plurality of attachment tabs are fixedly attached to said tubular self-expanding braided stent body.
 11. The apparatus of claim 8, wherein said distal stop member comprises an enlarged portion of said core advancement wire having a diameter greater than or equal to said first diameter of said compressed configuration of said distal expansion member.
 12. The apparatus of claim 8, further comprising a proximal stop member on said core advancement wire positioned outside and proximal to said proximal end of said tubular self-expanding braided stent body, said proximal stop member having a diameter greater than or equal to said first diameter of said compressed configuration of said distal expansion ring and less than a diameter of the delivery sheath.
 13. The apparatus of claim 8, wherein said intermediate stop member comprises an enlarged portion of said core advancement wire having a diameter greater than or equal to said first diameter of said compressed configuration of said proximal expansion ring. 